1. Field of the Invention
The present invention relates to an exhaust pressure regulating system for use with an exhaust gas recirculation system of an automobile.
2. Description of the Prior Art
An exhaust gas recirculation system (which will be hereafter referred to as "EGR" system) extracts exhaust gases from a portion of the exhaust system of an automobile and reintroduces the extracted gases into the intake system. The flow rate of the exhaust gases to be recirculated is conventionally dependent upon the gas pressure differential between the points of extraction and reintroduction of the exhaust gases.
Especially in an EGR system of the exhaust pressure control type, the quantity of exhaust gas recirculated is greatly influenced by the pressure level at the point of extraction. Since, on the other hand, the pressure at the extraction point varies not only with the diameter and shape of the engine exhaust pipe but also the variations in dimensions in the mass production of the exhaust pipe and the muffler, the quantity of exhaust gas recirculated becomes different among the automotive vehicles of the same type, thus inviting one of the major causes for the variation in the exhaust emission. Moreover, even if the automotive vehicle is equipped with the EGR system of exhaust pressure control type, the quantity of exhaust gas recirculated is reduced to a low level, during the low speed mode of operation of the engine at a low speed and a light load, due to reduction in the exhaust gas pressure. For this low speed mode or for light load operation of the engine, the EGR system will not begin to function easily, thus inviting difficulties in the exhaust gas emission control.